Botanical oils for edible and cosmetic use are produced for example by squeezing seeds of plants which have high oil content. Purification of botanical oils generally includes the steps of degumming, deacidification, bleaching, deodorizing, etc. by which phospholipids, free fatty acids, coloring matters, odorous substances, etc. are removed. Purified botanical oils are used in a wide variety of applications such as for edible and cosmetic uses.
Oils from plants generally include a plurality of polyunsaturated fatty acids with a varying number of carbon to carbon double bonds, such as monovalent (oleic acid 18:1), divalent (linoleic acid 18:2) and trivalent (alpha-linoleic acid 18:3), and the property of botanical oil is decided based on the composition of said fatty acids within the oil. Even in “camellia oils”, it is said that, in camellia oils originating from Camellia japonica, the content of oleic acid is 85 mass % (hereinafter, %) and the content of linoleic acid is 4.1%, whereas in camellia oils originating from Camellia sasanqua, it is said that the content of oleic acid is 83.3% and the content of linoleic acid is 7.4%. As shown above, camellia oils from Camellia japonica have a lower content of carbon-carbon double bonds compared to camellia oils from Camellia sasanqua (Oil and Oil ingredient Handbook (Yushi, Yuryou Handbook); Edited by Yoshiro Abe; Saiwai Shobo (1988)).
Parameter “iodine value” is used to identify the property of such fatty acid composition of botanical oils. Iodine value is an indication of the amount of carbon-carbon double bonds of polyunsaturated fatty acids, and when the iodine value is high, i.e. when a botanical oil comprises many polyunsaturated fatty acids, such oil is easily oxidized and has a tendency to discolor and denature. Therefore, in order to retain or raise the quality of the oil, hydrogenation is usually carried out during the degumming and/or the deacidification step to reduce the amount of carbon-carbon double bonds.
Most of the “camellia oils” that are currently commercially available use oils from Camellia oleifera produced in China as their ingredient. Oil of Camellia oleifera is positioned at about the center of oil of Camellia japonica and oil of Camellia sasanqua, and its iodine value is often slightly above 83. As described above, camellia oils with high iodine value are easily oxidized. Therefore, it is important to reduce the iodine value when producing purified botanical oils (for example, iodine value in the range of 78 to 83 in the case of camellia oil).
Among the aforementioned purification and hydrogenations steps of botanical oils, the most commonly used has been the purification with the application of heat. Examples of processing steps in heat-purification are as follows; degumming: water is added to raw oil and stirred with the application of heat after which phospholipids, etc. are removed following centrifugation; deacidification: the degummed oil is stirred under heat with sodium hydroxide after which free fatty acids are converted to soap and removed; bleaching: clay is added to the deacidified oil whereby coloring matters are removed; deodoring: the bleached oil is steam-distilled in vacuo by which traces of volatile odorous substances are removed (Oil and Oil ingredient Handbook (Yushi, Yuryou Handbook); Edited by Yoshiro Abe; Saiwai Shobo (1988)). In addition, there is also a hydrogenation step in which hydrogen is introduced into oil by which hydrogen is added to the unsaturated bond portion of the fatty acid, and this hydrogenation step is generally carried out at high temperatures, e.g. heating treatment at a high temperature of 230° C. is sometimes carried out for reactions for oil and hydrogen.
As shown above, the steps of purification and hydrogenation were mainly carried out at high temperatures, but such steps involving heating at high temperatures induce denaturation of fatty acid compositions and produces trans isomers which do not exist in nature. In recent years, researchers in countries throughout the world have pointed out that the intake of such trans fatty acids has negative effects on health, and first in Europe and then, in 2005, the United States have enforced a law requiring identification of content of trans fatty acids in edible oils. Awareness of danger of trans fatty acids is growing in Japan, and there is a need for a method for purifying and hydrogenating botanical oil without producing trans fatty acids.